Why do my plants have yellow leaves?

TL;DR : A variety of reasons, too much water, not enough water, diseases, insects, bacteria, nutrient deficiencies, cold drafts, ageing, renewal of leaves, lack of sunlight… Most of these can easily be solved but it might take a little time before your plants get back to their former health.

We’ve all encountered this very annoying problem at at least one point in our lives. Suddenly the leaves on your plant (or plants) seem to be turning yellow one by one for no apparent reason. At least not one you know of. This is probably why you ended up here.

Whether you’re a casual gardener or you only have one lonely house plant that your step-family gave you as a gift, you almost always feel a tinge of guilt seeing your plant less healthy than the luscious green it should be. We understand this feeling perfectly and this is why we will try to locate the source of your problem and get your plant back on its roots in no time!

To begin with you must know that there are quite a few reasons why your plant’s leaves could be turning yellow. Some of these reasons are totally benign, whilst some could cause permanent damage to your plant and may even lead to its death. In the following lines, we will review the most common reasons why your plants can be suffering from this discoloration.

1. Lack of water, not enough hydration
2. Insects or other pests
3. Chlorosis
4. Roots issues
5. Nutrient deficiencies
6. Lack of sunlight
7. Cold drafts
8. Normal ageing, renewal of leaves
9. Viral infection

Problem

Undewatering

Cause and identification

Your plant is thirsty, the soil at the base of the plant is dry if you stick your finger in it. Most plants in these conditions have droopy leaves. Citrus plant leaves on the contrary are heading upwards. There are a few ways to tell if your plants are getting too little water.

Solution

Water your plants more frequently or consider setting a dish at the bottom of the pot to keep the excess water for a little longer if your soil is draining the water very fast or the temperature is particularly warm and the air dry especially in summer. In extreme cases (for small plants) you can carefully immerse the whole pot in water. Be careful not to let the roots sit in water too long as this could cause them to rot. Some plants need quite high air humidity, or condensation on the leaves, especially to be able to cool off on the hottest summer afternoons (plants from wet tropical forests for example). Consider gently spraying the leaves with water in this case (but beware of wetting the leaves in direct sunlight which can lead to leaf scorch).

Lack of sunlight

Cause and identification

Your plant is not getting enough sunlight and cannot store enough energy to sustain its luxurious evergreen color. This is a common problem for indoor plants or during the long winter months in which daylight is sometimes scarce and the days are often much shorter.

If the yellowing begins on the side away from your light source, it might be caused by too little light reaching these back leaves.

Solution

Most plants need at least 4 hours of sunlight per day to stay perfectly healthy. This can be hard to attain during the winter.

A lot of plants are used to having a dormant period during the winter and can survive a few months per year with a limited amount of sunlight. Of course this is not beneficial to plants and there are alternatives to keeping your plants inside during the cold winter months.

Building a greenhouse to keep the warmth in during the winter can be a viable solution but there are many more to be discovered on this website.

If you are experiencing this problem and you feel like you have no better solution to provide sunlight to your green friends do not fret. Plants do not always require direct sunlight and there are ways to provide your plants with the adequate amount of light without adding new windows to your apartment or cutting down nearby trees.

Chlorosis

Cause and identification

Chlorosis is a condition in which leaves produce insufficient chlorophyll, turning them yellow. Chlorosis can be caused by a nutrient deficiency of iron—called iron chlorosis—or by a shortage or lack of magnesium or nitrogen. Soil pH sometimes plays a role in nutrient-caused chlorosis; many plants are adapted to grow in soils with specific pH levels and their ability to absorb nutrients from the soil can be dependent on this. Chlorosis can also be caused by pathogens including viruses, bacteria and fungal infections, or sap-sucking insects.

Chlorophyll is vital for photosynthesis, which allows plants to absorb energy from light.

Solution

If you happen to have a pHmeter you could test your soil’s pH level. Each plant has a preference for a specific pH. You can easily find your plant’s ideal pH requirements by searching the internet or asking us in the comments below and we will be sure to provide you with an answer in the best delays. This is one of the easiest way to solve most cases of Chlorosis.

Most plant thrive at a pH level around neutral (7) or in a slightly acidic soil. If you find that the pH level in your soil is not ideal for the plant you have in mind, there are ways to change the soil’s pH.

Many things can affect the soil’s pH. Watering your plants with tap water every day is one example. Depending on where you live your tap water can be slightly acid and over time lead to an acidification of soils.

Plants are greatly susceptible to highly alkaline (or basic) or acid pH.

Root issues / over-watering

Cause and identification

Your plants could have damaged or rotten roots. This sometimes happens during damp and cold winters. The roots are constantly sitting in moist soils that freezes during the subzero degree nights. The same problem can occur if your soil is constantly drenched and never has time to dry-out due to overwatering. This can also happen when your plants are pot-bound and have outgrown their current pots.

Sometimes the roots on plants with yellow leaves are growing out through the holes in the bottom of your flowerpot looking for nutrients and water, showing they need to be repotted.

Over-watering is probably the number one cultural fault that causes leaf yellowing. Very few plants appreciate water left to sit in their trays (called sublingual watering), and even tropical plants don’t want to grow in mud unless they are semi-aquatic plants so please do not drown your green friends. How would you feel if you were wearing wet clothes all day? The most dangerous time for over-watering is the winter when most plants are slowing down their metabolisms. The roots are more likely to freeze on cold nights if water is left sitting in their trays or pots.

Solution

For pot-bound plants the solution is simple. The roots are compacted too tightly in the container. The only way to solve this issue is either to prune the roots for bonsai plants for example or to repot this plant in a larger container or flower-bed (or to plant them directly in your garden). This is simple enough and will also cure damaged roots or roots that are tightly compacted. Use a larger pot and make sure to use new soil, leaving some soil around the roots. Once the plant is repotted, you just add water and make sure you watch the plant to see any improvements.

If the soil is too damp you should check the roots’ state by gently taking the plant out of its pot. Remove delicately all the rotten roots and change the soil to one that is more suited to the plant’s needs (in terms of soil drainage). Try to only water you plant when the top few centimeters of soil are totally dry. Over-watering a plant can be as deadly as underwatering one.

Nutrient deficiencies

Cause and identification

Plants may suffer from nutrient deficiencies because of poor soil or soil depletion (having used up all the soil’s resources). They may also suffer from lack of nutrients because they have become pot-bound and need a larger container. If you notice your plant is suffering from the latter we invite you to check the “Root issues” solution.

If the top leaves are yellowing, or if there is an unusual pattern to the yellowing (i.e., the veins remains dark while the tissue between them turns yellow), it is most likely a nutritional problem. This can be caused by too much calcium in the water, if you’re using hard water, or by a nitrogen deficiency.

Solution

Plants need to eat just like humans do. They require a vast array of nutrients in order the flourish. If your plant has been sitting in the same pot for a few years without new matter being added to the soil, then it might be slowly dying of hunger. The rates at which different plant absorb and deplete resources vary species to species. If you never give your plants fertilizer it might be a good time to start. Plants have different needs but most plants will be satisfied with compost or compost tea or even universal fertilizer in the correct quantities.

For the best effect you should research your plant’s needs on our website or on the web. If you would like you can ask us for our opinion in the comments below and we will be sure to provide you with an answer in the best delays.

Nutrient deficiencies may also occur because of inappropriate pH levels. To learn more about this read about pH levels here : there are ways to change the soils pH.

Pest problems

Cause and identification

If none of the solutions above seem to be applying to your problem then you might want to turn to one of the most aggravating problem a garden can have : a pest problem. You might want to look for some sort of pest infestation. Different bugs like different plants, and if your leaves are turning yellow, some bugs may have decided to set up camp in your plant causing this to happen. You might want to check if you have holes in your leaves as well. If so please check out our guide on garden pests.

Solution

It can be hard to identify which pest has settled in nicely but there are solutions that work against most pests.

There are homemade solutions that work on certain types of pests. Orange peels tend to ward off ants and rhubarb leave or black soap mixtures work for many pests. If you can identify the pest that is infesting your plant we recommend you look up the best treatment against this type of pest. If you would like you can ask us for our opinion in the comments below and we will be sure to provide you with an answer in the best delays.

While we cannot recommend you use bug spray because it can be dangerous for household pets, small children and other animals having access to your plants, it does work and won’t necessarily harm your plants if you wish to get rid of an infestation. If you intend to eat any part of this plant (medicinal or aromatic plants for example) then we deeply discourage the use of pesticides or insecticides.

Neem oil is one of the safest insecticides to use and will not harm you, your children or your pets. Of course you shouldn’t drink the stuff.

If you have a large enough variety of plants they should act as repellents for each type of pests protecting each other effectively and camouflaging the most vulnerable plants. You can check out which plants marry perfectly with each other on our website for some ideas.

Viral infection and other problems (fungi, …)

Cause and identification

Some bugs (a lot of pests) bring viral infections or illness along with them. For example cochineal allow a fungi name fumagine (a dark-colored sooty mold found chiefly on greenhouse plants or in southern latitudes and caused by various fungi of the order Erysiphales) to settle on your plant’s leaves. This is especially the case for Citrus trees.

We won’t blame the bugs for everything though will we? Many different viruses can infect plants. Certain crops are well known to be affected by virus diseases including geraniums, roses, Easter lilies, dahlias, gladiolus, and tulips. These can be “caught” by the plant in different ways, they can even get it from the soil they grow in as seedlings if it is contaminated. This is why many gardeners recommend cooking (microwaving or putting it in the oven) the substratum you are going use a growing medium before even putting your seeds in it.

There are other ways for plants to fall ill. These include :

• gardeners’ hands or tools. We carry diseases, we all know that, I mean our skin in literally crawling with bacteria (good, bad or undetermined). You should always try to clean your hands before and after gardening. More importantly: watch out for your tools. Often disease is transmitted from one plant to another if you use the same tools for pruning or for harvesting parts of your plants. Should as wash and wipe your tools when switching for when plant to another.
• aphids, thrips, whiteflies, leafhoppers, mites or nematodes feeding. We talked about cochineal a little higher but they are not the only insect that can make plants ill. Insects may weaken plants by feeding on them, leaving these plants more vulnerable to viruses. There are also other ways for them to transmit diseases. They may carry the disease themselves or honeydew (for aphids for example) may help sicknesses creep up on your plants. Honeydew is a sugar-rich sticky liquid, secreted by aphids and some others insects as they feed on plant sap. Heavily-infested leaves can wilt or turn yellow because of excessive sap removal. Some aphids are very important vectors of plant viruses. However, it is seldom possible to control these diseases by attempting to kill the aphid vectors with an insecticide. Aphids carrying viruses on their mouthparts may have to probe for only a few seconds or minutes before the plant is infected.
• through dodder (cuscuta) / parasitic plants. These may weaken to plant leaving it vulnerable to viruses of all sorts. Dodder is parasitic on a very wide variety of plants, including a number of agricultural and horticultural crop species, such as clover, potatoes, chrysanthemum, dahlia, trumpet vine, ivy and petunia. Of course these are just a few plants. Cuscuta can also spread plant diseases from one host to another if it is attached to more than one plant. Unless you are starting a farm or a homestead you will probably never meet cuscuta. In Europe for example there are only a few types of these vines.
• through grafting: every cut you make in a plant makes it more vulnerable to disease. It works exactly the same as for human beings. If you cut yourself your wound may get infected and fester. You may also introduce viruses by grafting an diseased branch on a healthy plant if you are not careful.

Symptoms vary with the virus involved, the species of plant infected, and the environmental conditions :

• slowed growth
• mosaic pattern of light and dark green (or yellow and green in our case) on the leaves
• malformation of leaves or growing points
• yellow streaking of leaves
• yellow spotting on leaves
• ring-spots or line patterns on leaves
• uniform yellowing or reddening of foliage
• flower color breaking
• crinkling or curling and crumpling of the edges of leaves.

Solution

As you now know the symptoms above can also be attributed to high temperature, hydration, insect feeding, mineral deficiencies or mineral excesses for example. This is why viruses often demand an expert’s opinion. Virus diseases cannot be diagnosed on the basis of symptoms alone.

• A viral infection might show up as blotchy, spreading yellow patches on leaves throughout the plant. There are also many other ways an illness may manifest its presence (you may also notice deformed leaves and stems and discolored flowers), but we are talking about leaves turning yellow here are we not? Viral infections in plants very hard to cure, so you’re better of trying to prevent them. They may infect all nearby susceptible plants. So if you fear one of your plants is infected you will probably want to quarantine it in case it starts spreading. Either try to learn more about what ails it (by getting an expert’s advice for example) or just discard plants you suspect of being infected.
• Cook / heat your growing medium (for small quantities of soil) before planting your seeds to get rid of any bacteria, insects, larvae or viruses living in it. This might not smell great. So be prepared. Let it cool down completely before using it, you don’t want to slow cook your seeds. This isn’t really a sustainable solution for large amounts of soil.
• Disinfect the tools you use for gardening as regularly as you can by placing them in a chlorine, hydrogen peroxide, or ammonium disinfectant for at least 10 min. Don’t forget to rinse and dry these well with a clean cloth.
• Plant disease resistant plants.
• Grow plants from seeds.
• Control your insect population. Learn more about this in our guide on garden pests.

Cold drafts

Cause and identification

Do you like cold drafts in winter? No-one really enjoys the cold air rushing past them, especially at night. Well, you can see how similar plants are to us, after all, we’re all living beings. So it probably won’t come as a surprise to you when we tell you that plants don’t either. Cold drafts on tropical plants especially (but harms some other plants as well) will often cause leaf yellowing and dropping.

Solution

If your plant is near an air-conditioning vent, move it to a less turbulent place and see if its leaves stop turning yellow. In winter, if you bring your plants inside or in a greenhouse make sure they are not in a cold draft.

Normal ageing / renewal of leaves

Cause and identification

Nothing to worry about here. If each of the yellow leaf areas are the lower, older leaves (while the newer ones remain green), then they are leaves whose time is over.  The plant is simply re-capturing the nutrients from the old leaves into the main plant and the leaves are therefore slowing discoloring before shriveling up and falling. They can go from green to yellow to brown sometimes before falling.

Solution

As many plants age, the lower leaves will turn yellow and drop off as a normal part of growth. This is especially true of foliage plants like dracaena. In this case, don’t worry. If the plant becomes too leggy, consider trimming back the main stem to promote new growth and bushiness. Otherwise just lay back and stop fussing your plant is doing just fine. Good job!

For most of these cases you should see improvements to your plants in a couple of weeks. To be sure we recommend you take a picture of your plant before and after to see if you notice any improvements.

If you’re not sure which one of these problems applies to your plants why not try to solve the easiest ones by moving your plants into a more sunlight spot, by giving it just a little bit more water (or by simply watering it more regularly) or giving it a little energy boost by giving it a bit of the appropriate fertilizer.

If there are any questions you would like to ask us, just do it below!

Thank you for reading!